The present invention relates to an ink jet recording apparatus which is capable of ejecting ink drops of different volumes through the same nozzle orifice, and more particularly to a method of driving an ink jet recording head of the ink jet recording apparatus.
The ink jet recording apparatus is composed of a recording head having linear arrays of nozzle orifices, a carriage mechanism for moving the recording head in the main scanning direction (a width direction of a recording paper), and a paper feeding mechanism for moving a recording paper in the subscanning direction (paper feeding direction).
The recording head includes pressure generating chambers communicated to the nozzle orifices, and pressure generating elements for varying ink pressures within the pressure generating chambers. In operation, a drive pulse is applied to each pressure generating element to vary an ink pressure in the associated pressure generating chamber, so that an ink drop is jetted from the related nozzle orifice.
The carriage mechanism moves the recording head in the main scanning direction. The recording head ejects ink drops through the nozzle orifices at times determined by dot pattern data, while moving in the main scanning direction. When the moving recording head reaches the terminal end of its moving range, the paper feeding mechanism moves a recording paper in the subscanning direction. Upon end of the recording paper movement, the carriage mechanism moves again the recording head in the main scanning direction. The recording head ejects ink drops while moving.
Repeating the above sequence of operations, the recording head records an image represented by dot pattern data on a recording paper.
The ink jet recording apparatus depicts an image on a recording paper by combinations of ejection and non-ejection of ink, viz., combinations of presence and absence of dots. For this reason, a half-tone method has been used in which one pixel is formed by a plurality of dots, for example, 4xc3x974 or 8xc3x978 dots. To print or visually recording an image at high quality on the recording paper by the half-tone method, it is essential to eject ink drops of extremely small volumes. Reduction of the volume of the ink drop creates another problem of reducing printing speed.
Achieving of the improvement of the print quality and increase of the printing speed is one of the important technical subjects currently imposed on engineers. There are some technical solutions, so far as we know, to this contradictory subject.
In the solution disclosed in, for example, Japanese Patent Publication No. 4-15735B and U.S. Pat. No. 5,285,215, a plurality of drive signal capable of generating fine ink drops are applied to the recording head. In turn, the recording head ejects a plurality of fine ink drops through the same nozzle orifice. In this case, the fine ink drops jetted are merged into a single large ink drop before those fine ink drops land on a recording paper.
The technical solution involves some problems to be solved, however. The number of fine ink drops that may be merged is limited. The result is that the volume of one ink drop, which results from the ink drop merging, may be increased with a limited ink volume and within a narrow range where the ink volume is variable. Further, control for merging fine ink drops into one large ink drop before they land on the recording paper is difficult.
A technical proposal is made in this connection. In the technique, a drive signal consisting of a succession of different drive pulses, which correspond to the volumes of fine ink drops to be jetted, is generated, and the drive pulses extracted from the drive signal are applied to the pressure generating element.
In the solution disclosed in the publications, mere connection of different drive pulses will create the following problems.
A first problem is that a drive period required for printing one dot is long. It is necessary to connect the number of drive pulses corresponding to the number of the different volumes of ink drops. The drive period is increased with increase of the number of drive pulses connected. The increase of the drive period leads to decrease of the printing speed.
A second problem is that the flying velocity of the ink drop depends on the volume of the ink drop. When comparing a large ink drop for forming a large dot with a medium ink drop for forming an medium dot, the flying velocity of the large ink drop is higher than that of the medium ink drop. Increase of the ink-volume difference leads to increase of the flying velocity difference. The flying velocity difference causes an incorrect landing position of the ink drop, resulting in degradation of the print quality.
The present invention is made to successfully solve the problems described above, and has an object to efficiently confine an increased number of drive pulses, which are capable of ejecting ink drops of different volumes, within a limited drive period.
Another object of the present invention is to lessen the flying velocity difference caused by the volume difference among the ink drops.
In order to achieve the above objects, according to a first aspect of the present invention, there is provided an ink jet recording apparatus comprising: a recording head including a pressure generating element provided in association with a pressure generating chamber communicating with a nozzle orifice, an ink drop is jetted from the nozzle orifice by applying a drive pulse to the pressure generating element; drive signal generating means for generating a drive signal; and drive pulse generating means for generating a drive pulse from the drive signal; wherein the drive signal generated by the drive signal generating means contains wave elements capable of activating the pressure generating element and a connection element incapable of activating the pressure generating chamber and for connecting connection ends of the wave elements having different voltage levels, and wherein the drive pulse generating means appropriately selects the wave elements in the drive signal and composes them into the drive pulse.
According to a second aspect of the. present invention, in the ink jet recording apparatus of the first aspect, the time period of the voltage-gradient portion of the connection element is not longer than that of the wave elements.
According to a third aspect of the present invention, in the ink jet recording apparatus of the first or second aspect, the wave elements include a plurality of ejection wave elements capable of driving the pressure generating element to eject an ink drop. The connection element interconnects the ejection wave elements.
According to a fourth aspect of the present invention, in the ink jet recording apparatus of the third aspect, the wave elements include a filling wave element capable of driving the pressure generating element to fill ink into the pressure generating chamber. The drive pulse generating means generates a plurality kinds of drive pulses at the time of selecting the ejection wave element and the filling wave element.
According to a fifth aspect of the present invention, in the ink jet recording apparatus of the first to fourth aspects, the wave elements include a plurality of ejection wave elements capable of driving the pressure generating element to eject ink drops at different timings. The drive pulse generating means generates a plurality of drive pulses such that an ink drop forming a small-volume dot is ejected earlier than an ink drop forming a large-volume dot.
According to a sixth aspect of the present invention, in the ink jet recording apparatus of the first to fourth aspects, the wave elements include a plurality of ejection wave elements capable of driving the pressure generating element to eject ink drops at different timings. The drive pulse generating means generates a small-dot drive pulse capable of ejecting a small-volume ink drop to form a small dot, a medium-dot drive pulse capable of ejecting a medium ink drop to form a medium-volume dot, and a large-dot drive pulse capable of ejecting a large ink drop to form a large-volume dot. Either one of ejection wave elements of large- or medium-dot drive pulses is located before an ejection wave element of a small-dot drive pulse on the time axis, and the other one is located after an ejection wave element of a small-dot drive pulse on the time axis.
According to a seventh aspect of the present invention, in the ink jet recording apparatus of the first to fourth aspects, the wave elements include first and second large-dot ejection wave elements capable of forming a large-volume dot, and an other-dot ejection wave element for ejecting an ink drop to form a dot having a size other than the large-volume dot. At least the other-dot ejection wave element is located between the first and second large-dot ejection wave elements. The drive pulse generating means generates a drive pulse containing the first and second large-dot ejection wave elements.
According to an eighth aspect of the present invention, in the ink jet recording head apparatus of the ink jet recording apparatus of the first to fourth aspects, the wave elements include a plurality of large-dot ejection wave elements for respectively ejecting a large ink drop forming a large-volume dot and an other-dot ejection wave element for ejecting an ink drop forming a dot having a size other than the large-volume dot, which is arranged between the large-dot ejection wave elements. The drive pulse generating means generates a drive pulse composed of at least one ejection wave element.
According to a ninth aspect of the present invention, in the ink jet recording head apparatus of the ink jet recording apparatus of the eighth aspect, the waveforms of the plurality of large-dot ejection wave elements are substantially the same with each other.
According to a tenth aspect of the present invention, in the ink jet recording head apparatus of the ink jet recording apparatus of the eighth and ninth aspects, two large-dot ejection wave elements are arranged in the drive signal so as to appear at a constant interval.
According to an eleventh aspect of the present invention, in the ink jet recording apparatus of the first aspect, the wave elements include a plurality of filling wave elements capable of driving the pressure generating element to fill ink into the pressure generating chamber, and an ejection wave element capable of driving the pressure generating element to eject an ink drop. The connection element interconnects the filling wave elements. The drive pulse generating means generates a drive pulse containing one selected filling wave element and an ejection wave element.
According to a twelfth aspect of the present invention, in the ink jet recording apparatus of the first to eleventh aspects, the connection element includes constant voltage portions at both ends coupled to the wave element.
According to a thirteenth aspect of the present invention, there is provided an ink jet recording apparatus comprising: a pressure generating element for expanding and contracting a pressure generating chamber in response to a drive pulse to vary an ink pressure within the pressure generating chamber in order to eject an ink drop from an nozzle orifice associated with the pressure generating chamber; drive signal generating means for generating for generating a drive signal; and drive pulse generating means for generating a drive pulse from the drive signal, the drive pulse generating means generating a first drive pulse containing an expansion wave element for expanding the pressure generating chamber and holding the expanded state of the pressure generating chamber, a first filling wave element for further expanding the pressure generating chamber expanded by the expansion wave element, and a first ejection wave element for contracting the pressure generating chamber expanded by the first filling wave element.
According to a tenth aspect of the present invention, in the ink jet recording apparatus of the fourteenth aspect, a time period for holding the expanded state of the pressure generating chamber is longer than the period of a natural period of the pressure generating chamber.
According to a fifteenth aspect of the present invention, in the ink jet recording apparatus of the ninth and tenth aspects, the drive pulse generating means generates a second drive pulse containing a contraction wave element for contracting the pressure generating chamber and holding the contracted state of the pressure generating chamber, a second filling wave element for expanding the pressure generating chamber contracted and held by the contraction wave element to fill ink therein, and a second ejection wave element for contracting the pressure generating chamber expanded by the second filling wave element to eject an ink drop.
According to a sixteenth aspect of the present invention, in the ink jet recording apparatus of the thirteen to fifteenth aspects, the expansion wave element consists of stepwise expansion wave elements for stepwise expanding the pressure generating chamber.
According to a seventeenth aspect of the present invention, in the ink jet recording apparatus of the thirteenth to sixteenth aspects, the contraction wave element consists of stepwise contraction wave elements for stepwise contracting the pressure generating chamber.
According to an eighteenth aspect of the present invention, in the ink jet recording apparatus of the thirteenth to seventeenth aspects, at least one of the drive pulses is divided into a plurality of wave elements in the drive signal. At least one other wave element for forming other drive pulse is located among the divided wave elements. The drive pulse generating means selectively composes the divided wave elements into a drive pulse.
According to a nineteenth aspect of the present invention, in the ink jet recording apparatus of the thirteenth to eighteenth aspects, the expansion wave element, which is to constitute at least one of the drive pulses, is divided into a plurality of expansion segments. At least one ejection wave element, which is to constitute at least one other drive pulse, is located among the divided expansion segments to form the drive signal.
According to a twentieth aspect of the present invention, in the ink jet recording apparatus of the thirteenth to nineteenth aspects, the contraction wave element, which is to constitute at least one of the drive pulses, is divided into a plurality of contraction segments. At least one ejection wave element, which is to constitute at least one other drive pulse, is located among the divided contraction segments to form the drive signal.
According to a twenty-first aspect of the present invention, in the ink jet recording apparatus of the eighteenth to twentieth aspects, an expansion segment constituting a part of the expansion wave element is located the front part of the drive signal. The first ejection wave element is located at the end part of the drive signal.
According to a twenty-second aspect of the present invention, in the ink jet recording apparatus of the eighteenth to twenty-first aspects, different voltage levels of the divided wave elements are mutually connected by the connection element.
According to a twenty-third aspect of the present invention, in the ink jet recording apparatus of the first to twenty-second aspects, the pressure generating element is a piezoelectric vibrator of the flexural vibration type.
According to a twenty-fourth aspect of the present invention, in the ink jet recording apparatus of the first to twenty-second aspects, the pressure generating element is a piezoelectric vibrator of the longitudinal vibration type.
According to a twenty-fifth aspect of the present invention, in the ink jet recording apparatus of the first to twelfth and twenty-second aspects, the pressure generating element includes a piezoelectric vibrator of the longitudinal vibration type. An end point of the wave element for decreasing the voltage from a medium voltage is set at a voltage level within a range of 5V from a ground potential and connected to the connection element.
According to a twenty-sixth aspect of the present invention, there is provided a method of driving an ink jet recording apparatus comprising the steps of: generating a drive signal containing divided wave elements mutually connected by at least one connection element; selecting wave elements located before and after the connection element on the time axis; composing the selected wave elements into a drive pulse; and applying the generated drive pulse to an pressure generating element to eject an ink drop.
According to a twenty-seventh aspect of the present invention, there is provided a method of driving an ink jet recording apparatus comprising the steps of: generating a drive pulse for expanding the pressure generating chamber, holding the expanded state of the pressure generating chamber for a predetermined time period, further expanding the expanded pressure generating chamber and contracting the further expanded pressure generating chamber; and applying the drive pulse to a pressure generating element to eject an ink drop.